The Test

How is it used?

The white blood cell differential is often used as part of a complete blood count (CBC) as a general health check. It may be used to help diagnose the cause of a high or low white blood cell (WBC) count, as determined with a CBC. It may also be used to help diagnose and/or monitor other diseases and conditions that affect one or more different types of WBCs.

The five types include: neutrophils, lymphocytes, monocytes, eosinophils and basophils. The differential totals the number of each type and determines if the cells are present in normal proportion to one another, if one cell type is increased or decreased, or if immature cells are present. This information is useful in helping to diagnose the specific cause of an illness, such as:

Some diseases trigger a response by the immune system that causes an increase in certain types of WBCs. A differential may give clues to the specific cause of that immune response. For example, it may help determine whether an infection is caused by bacteria or by viruses.

Other conditions affect the production of certain WBCs by the bone marrow or their survival in the circulation, resulting in either an increase or decrease in their number. A differential informs the doctor as to which type of WBC is low or high.

An abnormal differential result may be followed by other tests such as a blood smear, bone marrow biopsy or immunophenotyping (e.g., flow cytometry). These tests can reveal the presence of abnormal and/or immature populations of WBCs.

What does the test result mean?

The results indicate the number and/or the percentage of each type of white blood cell that is present in a person's sample of blood.

Results of a differential are usually reported as absolute values of the five types of WBCs and/or may be reported as a percent of the total number of WBCs. Absolute values are calculated by multiplying the total number of WBCs by the percentage of each type of white cell. This information can aid in diagnosing illness and monitoring therapy. Neutrophils typically make up the highest number of WBC, followed by lymphocytes, then monocytes, eosinophils and basophils.

Care must be taken when interpreting the results of a differential. A doctor will consider an individual's signs and symptoms and medical history as well as the degree to which the cells are increased or decreased. A number of factors can cause a transient rise or drop in the number of any one type of cell. A persistent increase or decrease will usually prompt further testing to determine the cause.

The following table gives some examples as to what the results of a differential may indicate:

As with eosinophils, numbers are normally low in the blood; usually not medically significant.

In certain cases, immature and/or abnormal forms of the cells may be present in the blood and may be detected with a differential. Immature forms include metamyelocytes, myelocytes, promyelocytes, and/or blasts. Further work-up (e.g., bone marrow biopsy) may be necessary.

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This article was last reviewed on May 9, 2012. | This article was last modified on June 25, 2015.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.